The present invention relates to an arrangement for ensuring the functioning of a brake by distribution of braking action selectively to the vehicle wheel configuration for a vehicle.
That the brakes of a vehicle, e.g. a heavy vehicle, function as intended is of the greatest importance, particularly today, when the total weights of heavy vehicle combinations (e.g. truck and trailer) are increasing and hence also the axle pressures of the respective vehicle combinations. In addition, average speeds are higher and timetables tighter. Traffic density is increasing. All this results in heavy demands upon the brake systems of heavy vehicles, particularly that they should function as intended.
Conventional trucks use pneumatic configurations for controlling the braking process. More recent trucks use electronics for controlling the braking process. Compressed air is only used for applying the wheel brakes, which may include disc brakes or drum brakes, one wheel brake for each wheel. The driver of a heavy vehicle can communicate with the electronically controlled brake system via some brake control, preferably the brake pedal. Such electronically controlled brake systems may also incorporate load sensors designed to measure, for example, the vehicle's respective axle weights or total weight. The electronically controlled brake system is designed to communicate with the pneumatic configuration which is designed to control the brake cylinders of the respective wheel brakes. The brake cylinders are connected to the friction linings of the respective wheel brakes which are intended to act upon, for example, a brake disc or a brake drum. In such electrically controlled brake systems, all the wheel brakes are usually applied simultaneously. However, the brake system may be designed in such a way that the brake pressure delivered to one wheel brake of the vehicle differs from the brake pressure delivered to another wheel brake of the same vehicle, with a view to maintaining vehicle stability. This method is used in order, inter alia, to prevent skidding and overturning of the vehicle, e.g. if the brake action called for by the driver on a sharp bend would result in too much brake action on an individual axle, the brake system may be designed in such a way that the brake action called for is limited. Electronically controlled brake systems of the aforesaid type may also incorporate ABS control, i.e. the brake action called for by the driver being limited by the available friction between ground and tires with a view to preventing wheel locking. In addition, an electronic brake system of the aforesaid type may incorporate functions to prevent wheel spin. Many electronically controlled brake systems incorporate at least one additional brake, e.g. a retarder which generates an outward braking moment by means of, for example, viscous friction. Such a retarder may be arranged to brake the universal shaft of the vehicle concerned. Further examples of supplementary brakes which may be included in an electrically controlled brake system are exhaust brakes and compression brakes which increase the engine's natural braking effect.
Light braking and recurring light braking by means of the wheel brakes, particularly where the wheel brakes incorporate disc brakes, may reduce the friction between discs and linings. This may lead to the driver finding the vehicle difficult to brake and hence possibly to the driver pressing the brake pedal harder, which may lead to unnecessarily great brake action, so-called overbraking.
Said reduction in friction between discs and brake linings depends on the brake lining material. The reduction in friction may be due, inter alia, to changes in the brake lining material which may arise because of low thermal and mechanical loading, particularly during light braking. This may result in the formation of a film which accumulates on the brake lining surfaces. The film accumulating on the brake lining surfaces which make contact with the disc causes reduction in friction between discs and brake linings. It is also possible for brake lining material to react with the road surface, e.g. with salts, in which case a film may form and accumulate on the brake lining surfaces and hence reduce the friction between discs and brake linings. Said film may thus, at least at an initial stage of brake application, reduce friction between brake linings and brake devices.